Answer:
Jia Jia = 6 years
Kai Kai = 7 years
Step-by-step explanation:
J + K = 9
K = J + 1
J = 2012 Jia Jia age
K = 2012 Kai Kai age
Replacing the second equation on the first equation:
J + (J+1) = 9
2J + 1 = 9
2J = 9 - 1
2J = 8
J = 8/2
J = 4 years
K = J+1
K = 4 + 1
K = 5 years
then:
2014 - 2012 = 2
J = 4 + 2 = 6 years
K = 5 + 2 = 7 years